Method of making synthetic textile yarn



Oct. 7, 1969 c. w. KIM 3,470,59

METHOD OF MAKING SYNTHETIC TEXTILE YARN Filed March 30. 1967 EXTRUDE RFIG 3 29 29 FIGJI l9 FIGS 7 '0 CHARLES W.

- INVEN AGENT United States Patent 3,470,594 METHOD OF MAKING SYNTHETICTEXTILE YARN Charles W. Kim, Heritage Park, Del., assignor to HerculesIncorporated, Wilmington, Del., a corporation of Delaware Filed Mar. 30,1967, Ser. No. 627,104 Int. Cl. D02g 3/34, 1/16 US. C]. 28-72 2 ClaimsABSTRACT OF THE DISCLOSURE The present invention relates to a method ofmaking a yarn of synthetic polymers and particularly to yarn formed froma relatively narrow strip or ribbon of film, which yarn, while itconsists of continuous filaments, has a so-called spun look, that is, abulky appearance characterized by a plurality of fiber ends extendinglaterally from the yarn in the manner of the fiber ends in a yarn spunfrom short length fibers or staple.

In the most commonly used methods employed in the production ofsynthetic yarn, the yarn is formed from a plurality of continuousfilaments that are simultaneously extruded in a molten condition and aremelt drawn to a reduced diameter. The filaments are subsequently drawnat an orienting temperature, which drawing further reduces the diameterof the filaments and imparts strength thereto. The filaments are thentwisted into yarn. The linearity and surface characteristics of thefilaments so formed affect the yarn both in physical properties (e.g.,strength, filament density, and frictional and thermal characteristics)and in appearance (e.g., bulk, softness or hand, and lightreflectivity). To modify the appearance and physical properties of theyarn, the yarn is usually further processed through a bulking orcrimping operation wherein a permanent crimp is imparted thereto.

Yarns have also been produced from synthetic fibers by cutting thecontinuous filaments, usually in the form of tow, into short lengths orstaple and processing them, for example, in the same manner as cottonand wool fibers are normally processed. Yarns so produced have anapparent breaking strength that is reduced relative to continuousfilament yarns of comparable denier and are more expensive to process,but they can be formed of different fibers blended to achieve variouseffects, and have improved appearance and hand relative to thecontinuous filament yarns.

Processes have also been developed heretofore for producing continuousfilament synthetic yarns from uniaxially oriented plastic film in theform, for example, of narrow strips slit from a wide sheet of film. Insuch processes, the film is reduced to filaments to form a multifilamentyarn by mechanical working such as by brushing, rolling or twisting, orby the action of an air jet. Because handling and working a film isgenerally easier than handling or working a plurality of individualfilaments, it is usually less expensive to produce continuous filamentyarn from film than from individually formed filaments. However, withfilaments formed from film, there is no control of the width of thefilaments other than the inherent weakness of the film in the directiontransverse to the direction of orientation. Thus, there are appreciablevariations in the width of the filaments along their lengths, withcorresponding variations in the strength, hand and appearance of theyarn, and there are many broken or run-out filament ends.

In making continuous filament yarn from film, an advantage of using ajet of air to separate the film into individual filaments rather thanmechanical working is that the jet not only splits the film but theturbulence thereof also acts to intermingle the filaments, whichcontributes to the cohesiveness of the yarn. and reduces the twistingrequired to form the filaments into a yarn. There is also a certainnumber of filaments broken to produce ends that, in the yarn, projectlaterally in the manner of the fiber ends in a spun yarn so that theyarn formed from these filaments tends to simulate the appearance of aspun yarn. In such a yarn, however, since the ends are formed by brokenfilaments, the strength of the yarn is reduced relative to the strengthof a corresponding yarn of continuous or unbroken filaments and thenumber of such filament ends that can be accommodated is thereforelimited. At the same time, since the ends generally correspond in crosssection to the cross section of the filaments, they tend to berelatively coarse and thus their effect upon the hand or softness of afabric produced from such a yarn is limited. Examples of the use of anair jet for splitting an oriented film into filaments are found inPatents Nos. 3,214,899 and 3,242,035.

It has also heretofore been proposed to produce synthetic yarn fromstrips of striated film, that is, from film having a plurality of spacedparallel longitudinally extending filament-forming portions orstriations that are generally circular in cross section and areconnected together longitudinally by integral webs of reduced thickness.Such films may be used in ribbon form, as illlustrated in Patent No.3,164,948, or in a random or partial split form as disclosed, forexample, in Patent No. 3,273,- 771 and in Japanese patent publicationNo. 16,450/65. Yarns formed in this manner have generally been formedfor the purpose of obtaining more flexible yarns than were obtainable byconventional melt-spinning processes, that is, in comparing a striatedribbon with a monofilament of comparable denier, the individualstriations of the ribbon are smaller as well as easier to form on acommercial basis and the yarn is also more flexible. Among the otheradvantages of striated film, the webs define lines of weakness wherebythe film can be readily split along the webs as by tearing or brushing.A further advantage of striated film is that, with a limited amount ofsplitting at the web and the individual striations or filaments thusconnected together by the unsplit portions of the web, a reduced amountof twisting is required to form the filaments into a yarn.

Notwithstanding the fact that the prior art includes various methods forsplitting film into filaments, various attempts to produce a bulkyappearance in a continuous filament yarn, and various examples of theuse of striated film, for example in making cordage, there has notheretofore been produced a synthetic yarn having tensile strengthsubstantially equal to a continuous filament yarn of comparable denierwhile having the appearance and hand of a spun yarn, and having improvedbulk and the corresponding covering, thermal and frictionalcharacteristics.

Accordingly, the objects of this invention are to provide a method formaking a bulky synthetic yarn having the appearance and hand resemblingthat of a yarn spun from staple and having improved covering capacity,insulation and tensile strength.

A further and specific object of this invention is to provide a methodfor making a continuous filament synthetic yarn having a plurality oflaterally projecting side hairs or fibrils of reduced cross section andwherein the number and length of such side hairs or fibrils arerelatively large.

A further object of this invention is to provide a method for producinga synthetic yarn in accordance with the above objects, which method isinexpensive to practice, which reliably produces a quality product, andwherein the length and number of the side hairs or fibrils on thefilaments can be controlled to produce various effects.

In accordance with the method of this invention, the above objects havebeen achieved by providing a strip or ribbon of striated film that ishighly oriented uniaxially in the longitudinal direction, which strip issplit into a plurality of individual filaments by a jet of air or otherfluid impinging upon the strip in a direction substantially normal tothe ribbon. When a strip of film having a cross section in accordancewith this invention is acted upon in this manner, the film splitslengthwise along each of the webs with surprising regularity and with nodiscerniblc migration of the splitting across any of the striations.Thus, there is produced a yarn in which the individual continuousfilaments formed from the striations are very uniform in cross sectionlengthwise of the filaments. At the same time, there is formed from thewebs a plurality of fibrils or side hairs on each of the filaments,which fibrils have a reduced cross section relative to the cross sectionof the filaments. The number of fibrils and the length of them as wellas the efiiciency in the separation of the striations are primarily afunction of the dimensions of the striated film and its cross sectionalprofile, the degree of orientation, the characteristics of the jet, thecharacteristics of the polymer such as its molecular weight, and theprocess conditions such as the temperature of the film.

For a more complete understanding of this invention, a preferredembodiment thereof is hereinafter disclosed with reference to theaccompanying drawings, in which:

FIG. 1 is a schematic illustration of equipment employed in making astriated film in accordance with this invention.

FIG. 2 is a schematic illustration of equipment employed in orientingand fibrillating striated film.

FIG. 3 is a fragmentary detail sectional view of the die lips of theextruder illustrated in FIG. 1.

FIG. 4 is a fragmentary detail cross sectional view of a striated filmapproximately as it may appear immediately upon extrusion from the dielips of FIG. 3.

FIG. 5 is a view similar to FIG. 4 of the striated film after it hasbeen melt drawn.

FIG. 6 is a view similar to FIG. 5 of the striated film after it hasbeen oriented.

FIG. 7 is a view of the striated film of FIG. 6 after fibrillation.

FIG. 8 is a fragmentary plan view of the yarn of FIG. 7.

FIG. 9 is a fragmentary view on an enlarged scale of one of thefilaments of the yarn of FIG. 7.

FIG. 10 is a cross sectional view taken substantially on the line 10-10of FIG. 9.

FIG. 11 is a view similar to FIG. 3 but illustrating the die lips formaking a single striated film strip.

In the drawings, there is illustrated schematically a conventionalextruder 1 having a hopper 2 at the input thereof. At the discharge endof the extruder 1 there is a metering device 3 having a discharge die 4from which issues the as-extruded film strip 5a illustrated generally inFIG. 4. Immediately upon issuing from the die 4, the film strip 5a ismelt drawn, the melt-drawn film strip being designated at 5. Themelt-drawn film strip 5 is quenched, for example, in a quench tank 6that is filled with a liquid, which may be water at tap temperature. Themelt drawn of the film strip may be in the range of 3:1 to 10:1 orhigher.

Located within the quench tank 6 are idler rolls or bars 7 for directingthe film strip 5 to a pair of feed rollers 8 that efi'ect the melt drawof the film strip. The rollers 8 operate at a peripheral speedsuificiently high relative to the speed at which film strip 5a isextruded to produce the desired melt draw of the strip 5. Asillustrated, from the feed rollers 3, the film strip 5 is wound to forma film roll 9, although the film strip 5 could of course he led directlyto a subsequent operation in a continuous process without intermediatewinding and unwinding.

As illustrated in FIG. 2, the melt-drawn film strip 5 is pulled from thefilm roll 9 by a set of low-speed feed rollers 10. Between the low-speedfeed rollers 10 and a comparable set of high-speed draw rollers 11, thefilm strip 5 is directed over a heated drum 12, a pair of idler rollers13 and 14 and a cold drum 15. The heated drum is maintained at atemperature sufiicient for heating the film strip to the optimumorienting temperature for the particular material and which, forexample, may be about C. for a film strip of polypropylene. The colddrum 15 is maintained at ambient temperature. The high-speed drawrollers 11 are operated at a peripheral speed relative to the low-speedfeed rollers 10 to provide the desired draw ratio, which for example maybe up to about 15:1, and with a melt draw ratio of about 4:1, ispreferably about 6:1 or 8:]. Drawing the film strip occurs between thehot drum 12 and the first idler roll 13. The oriented film strip isdesignated 16. After drawing, the strip 16 is cooled by the cold drum15.

The oriented film strip 16 is pulled from the delivery end of the drawrollers 11 by a pair of feed rollers 17. Between the rollers 11 and 17,there is a fibrillation device 18 that separates the film strip 16 intoa yarn 19 that consists of a bundle of individual continuous filaments.From the rollers 17, the yarn 19 is taken up into a yarn package 20.

The fibrillation device 18 comprises a cylinder 21 having guides 22 inthe opposite ends thereof and an air tube 23 in the side wall thereof.The guides 22, as illustrated, are in the form of plugs inserted intothe ends of the cylinder and having central bores that serve as theguides for the incoming film strip 16 and the outgoing yarn 19. The airtube 23 comprises a tube arranged substantially radially of the cylinder21 and located near the longitudinal center of the cylinder, the tubebeing connected at one end to a source of air under pressure (not shown)and at the other end to the interior of the cylinder 21 through anaperture in the side Wall thereof.

In FIG. 3 there is illustrated in cross-section a portion of one set ofdie lips 24 for the die 4 for producing the film strip 5a. As shown, thedie lips 24 have a matched series of opposed die grooves 25 equallyspaced along the length thereof and separated by intermediate die faces26. In their operative relation in the die 4, the die lips 24 arepositioned with the opposed die faces 26 slightly spaced. Thus, asillustrated in FIG. 4, the film strip 5a comprises a plurality ofsubstantially rounded filament-forming strips 27, which are hereinreferred to as the striations and which are arranged in spaced parellelrelation and are interconnected by integral webs 28. In FIG. 5, themelt-drawn film strip 5 is illustrated in cross-section and as showncomprises a series of striations 29 and webs 30 correspondingrespectively to the striations 27 and webs 28- of the film strip 5a. Therelative dimensions of the film strips 5a and 5, as shown in FIGS. 4 and5, roughly represent a melt-draw ratio of about 4:1. The oriented filmstrip 16 is illustrated in cross section in FIG. 6 and comprises aseries of striations 31 and Webs 32 corresponding respectively to thestriations 27 and webs 28 of the as-extruded film strip 5a. The relativedimensions of the film strips 5 and 16 represent a draw ratio of about6:1. In FIG. 7, there is illustrated in cross section a portion of theyarn 19.

As shown in FIG. 7, the film strip 16 has been split longitudinally ofthe webs 32 into a plurality of filaments 33. In FIGS. 9 and 10, thereis illustrated somewhat schematically and on an enlarged scale a typicalfilament 33 of the yarn 19. This filament comprises an individualstriation 31 together with a portion of the web 32 on each side thereof,which web portions terminate in side edges 34 and which constitute theedges along which the Webs 32 have been slit to separate the respectivefilament 33 from its adjacent filaments on the film.

'Ihe filament 33 has a shape that is generally round or, moreparticularly, has a maximum thickness substantially at its transversecenter between an upper edge 35 and a lower edge 36. Outwardly in bothdirections from the edges 35 and 36, the thickness of the filamentdecreases to the minimum thickness at the side edges 34 equal to thethickness of the web 32 in the oriented film strip 16. The configurationof the side walls of the filament 33 intermediate the edges 34, 35 and36 is a function of the draw ratios in the melt-draw and in theorientation and, with the film 5a as illustrated in FIG. 4, may besubstantially circular as shown in FIG. 10. Lengthwise of the filament33, the thickness between the edges 35 and 36 and the width between theopposite side edges 34 are substantially uniform.

In addition to the fact that the film strip 16 has split into aplurality of individual continuous filaments 33 substantiallycorresponding in number to the number of striations 31, the webs 32 haveformed a plurality of fibrils or side hairs 37, FIG. 9, at the opposedside edges 34. Under the action of the air jet, the fibrils 37 are tornloose or run-out at one end from one of the two filaments between whichit is formed and so define side hairs of varying lengths. Each of theside hairs 37 has a cross section that, except where broken, decreasesfrom the base to a point at the free end. This apparently results fromthe lateral wandering or migration of the molecular orientation in thefilm between two adjacent filaments that is present even in highlyoriented film. Since each fibril 37 has a thickness comparable to theoriginal thickness of the web 32 from which it was formed and a widththat at the base may be roughly equal to its thickness, the fibril 37 issubstantially finer than a filament 33.

In the yarn 19, the number of filaments 33 corresponds to the number ofstriations 31 in the film strip 16 and this in turn is determined by thenumber of die grooves 25 in the die lips 24. Inasmuch as the filaments33 are all continuous and are not broken, the tensile strength of theyarn is determined by the polymer characteristics and is not dependentupon the degree of twist in the yarn as are yarns of staple or of brokenfilaments. Accordingly, twisting of the yarn is not necessary forpurposes of strength so the amount of twist imposed upon the yarn needbe no more than that required to establish coherence of the yarn, whichrequires a low level of twist, and can otherwise be selected for otherdesired effects. From this standpoint, since a high twist is notrequired, the yarn can be made quite loose and bulky with the resultingadvantages of improved covering capacity and increased insulation for agiven weight of yarn.

The fibrils or side hairs 37 of the filaments 33 contribute to the aboveadvantages. Inasmuch as the fibrils 37 extend laterally relative to thefilaments 33, they tend to support the filaments in spaced relation toincrease the bulk of the yarn relative to a comparable yarn of equaltwist but without the fibrils. At the same time, the fibrils increasethe covering capacity of the yam and the insulation.

The free ends of the fibrils 37 extending from a fabric formed from theyarns 19 adds a softness to the surface of the fabric as well as createsthe appearance of a fabric formed from spun yarn. The fineness of thefibrils 37 increases the softness of the fabric. With fiber ends formedby the fibrils or side hairs 37, the breaking strength of the yarn isgreater than it would be if they were formed by broken filaments.

A more complete understanding of the present invention will be had fromthe following specific example of one yarn-forming process. Apolypropylene film was extruded through a die having die lips as shownin FIG. 3, the die lips having semicircular die grooves 25 with a radiusof 6 mils and 30 mils from a point on one groove to the correspondingpoint on the adjacent groove. The die faces 26 were 18 mils wide andwere spaced a distance of 2 mils from the corresponding die face 26 0fthe opposite die lip 24. The total width of the die lips 24 was 2 inchesand there were 67 of the die grooves 25.

The as-extruded film strip 5a was melt drawn at a ratio of 4:1 toprovide a melt-drawn film strip 5 having a total width of about 1.5inches and striations 29 having a total thickness of about 5 mils. Thestrip 5 was oriented at a draw ratio of about 6:1 to provide theoriented film strip 16 having an overall width of about 0.7 inch, havingstriations 31 with an average total thickness of about 1.5 to 2.5 milsand a gauge or a distance from a point on one striation to thecorresponding point on the adjacent striation of 10 mils, and havingwebs 32 with an average thickness of 0.5 to 1.0 mil.

The film strip 16 was fed through a fibrillation device 18 comprising acylinder 21 that was 6 inches long and had an internal diameter of 0.75inch, and had an aperture at the center thereof that was connected to anair tube 23 arranged radially of the cylinder 21 and having an internaldiameter of 0.125 inch. Air at 40 p.s.i.g. was supplied to the tube 23.There was a slight over-feed, for example, five percent, of the drawrollers 11 relative to the feed rollers 17, so that there was limitedplay of the film strip 16 in the cylinder 21. The film strip 16 wassubstantially completely reduced to individual filaments correspondingto the striations 31 of the film strip and there was no discerniblemigration of the splitting across any of the filaments so that all ofthe filaments were in fact continuous. On each filment, there was anaverage of about 6 fibrils 37 per inch, equally divided between theopposite sides thereof, which fibrils had an average cross section ofabout 0.5 mil compared to a filament diameter of about 3 mils, andvaried in length from about H inch to about inch, with an average lengthof about A; inch.

The yarn 19 can be formed of any polymer that can be extruded and drawninto an oriented striated film, for example, polyethylene,polypropylene, and copolymers of ethylene and propylene.

The yarns in accordance with the method described above aresubstantially linear, but, for the usual reasons, for example,resilience and covering capacity, may be bulked in any conventionalbulking process such as stufiing box or knife edge crimping.

The number as well as the width and length of the fibrils 37 can becontrolled by control of the width of the web 28 in the film 5a, thedegree of orientation, the tension on the yarn at fibrillation, thedirection and velocity of the jet, the polymer characteristics and theoperating or process characteristics. Generally, a wider web in the filmand more linear orientation lengthwise of the web will provide a greaternumber of and longer fibrils. As the tension on the yarn duringfibrillation is increased, the number of hairs and lengths of them arereduced because the film is afforded less opportunity to wave or vibraterelative to the air jet and thus to be worked repeatedly by the jet.When the jet is directed lengthwise of the film rather than transverseto it, the degree of fibrillation or separation is reduced.

While the film strip is herein disclosed as extruded as a strip, it willbe obvious that it could be formed either as a flat sheet or tube andsubsequently slit into strips of the desired width.

While air is preferably used for the jet for the fibrillation of thefilm, it will be obvious that the jet may be provided by a gas or fiuidother than air.

The degree of fibrillation or separation of the film into filamentsunder given circumstances can be increased if necessary by providing asecond fibrillation device 18 arranged in tandem relative to the firstdevice.

It will of course be apparent that the specific configuration of thestriations 27 is not critical. Rather than circular as herein disclosed,they could for example be substantially diamond-shaped or square. At thesame time, the striations could be single rather than double, that is,they could extend in one direction only from the web rather than in bothdirections from the web 28 as illustrated in FIG. 4. In FIG. 11, thereis illustrated a die lip 40 for making a single striated film, which dielip comprises a plurality of die grooves 41 adapted to cooperate with aflat or straight die lip 42. The single striated film has the advantagethat it can be cooled by running it over a chilled roll and canotherwise be handled by engaging the flat face thereof without crushingor otherwise damaging the striations. Since the die grooves 41 areformed in only one of the die lips, the die lips are less expensive andthe alignment of the die grooves 25 that is necessary in the opposed dielips 24 for making double striated film has been eliminated.

What I claim and desire to protect by Letters Patent is:

1. A method for making a bulky synthetic yarn having a spun-likeappearance, said method comprising the steps of providing a film stripthat is highly oriented uniaxially and has a plurality of spacedparallel striations longitudinally aligned with the axis of orientationand webs integral with and extending between said striations, passingsaid film strip through a pair of spaced film guides, and separatingsaid film strip at a point intermediate said guides along said webs withthe formation of fibrils from said webs by directing a fluid jet ontosaid film strip in a direction substantially normal to said strip offilm thereby reducing said strip of film to a plurality of individualfilaments consisting of individual striations together with a portion ofthe web at each side edge thereof and fibrils integral with saidfilaments at said side edges and extending laterally therefrom.

2. A method of making a bulky synthetic yarn having a spun-likeappearance, said method comprising the steps of providing a film havinga plurality of spaced parallel striations and webs integral with andextending between said striations, imparting to said film linearorientation with the axs of orientation aligned longitudinally of saidstriations, passing a strip of said film through a pair of spaced filmguides, and separating said film strip at a point intermediate saidguides along said webs with the formation of fibrils from said webs bydirecting a fluid jet onto said film strip in a direction substantiallynormal to said strip of film thereby reducing said strip of film to aplurality of individual filaments consisting of individual striationstogether with a portion of the web at each side edge thereof and fibrilsintegral with said filaments at said side edges and extending laterallytherefrom.

References Cited UNITED STATES PATENTS 3,177,557 4/1965 White 28-723,214,899 11/1965 Wininger 57-140 3,273,771 9/1966 Beaumont 57-140 XR3,336,174 8/1967 Dyer et al 28--72 XR JOHN PETRAKES, Primary ExaminerU.S. Cl. X.R. 28l; 57-157

